Abstract : The design and implementation of the NPS LISP programming system is described. NPS LISP is an interactive version of LISP 1.5, a sophisticated list processing and symbol manipulation computer language. NPS LISP was implemented in PL/I for operation under the CP/CMS time-sharing system on the IBM 360/67 computer. It is an interpretive system patterned after 7090 LISP. Most of the features of 7090 LISP are included in NPS LISP.